1. Field of the Invention
This invention relates to a process for producing a cyclic urea expressed by the formula (I) ##STR2## wherein R represents a lower alkyl group and R' represents a lower alkyl group-substituted dimethylene group, trimethylene group, a lower alkyl group-substituted trimethylene group, tetramethylene group or a lower alkyl group-substituted tetramethylene group, by reacting a diamine with urea.
Cyclic ureas of the formula (I) such as 2-imidazolidinones, tetrahydro-2(1H)-pyrimidinone, hexahydro-2H-1,3-diazepin-2-ones, etc. are useful substances as non-protonic polar solvents and as an intermediate for pharmaceuticals, pesticides, etc. Particularly the cyclic ureas are superior solvents for high molecular compounds such as polyamides, polyvinyl chloride, polyvinyl alcohol, polystyrene, polyurethanes, phenolic resins, etc. and also are easily soluble in many inorganic compounds and further are used as a solvent for various characteristic organic reactions.
2. Description of the Related Art
As to the process for production of the above-mentioned cyclic ureas using a diamine and urea, some processes have been proposed. For example, as to production of 1,3,4-trimethyl-2-imidazolidinone, there has been known a process of reacting N,N'-dimethyl-1,2-propanediamine with urea to obtain the objective product with a yield of 75% [Liebig, Ann. der Chem., vol. 726, page 97 (1969)]. However, this process uses an excess quantity of the diamine, that is, 1.5 mol per mol of urea in order to improve the operation of the reaction mass and the yield. Since such an excess diamine is expensive, it is necessary to recover it from the reaction mass. Further the yield of 75% is still unsatisfactory in the aspect of commercial production process.
Further, a process has been known wherein N,N'-diethyl-1,3-propanediamine or N,N'-dipropyl-1,3-propanediamine is reacted with urea to obtain 1,3-diethyltetrahydro-2(1H)-pyrimidinone or tetrahydro-1,3-dipropyl-2(1H)-pyrimidinone with a yield of 64.0% or 21.5%, respectively (J. Med. Chem., vol. 14, page 140 (1971)). These processes are also commercially unsatisfactory due to the low yields of the objective products.